1. The Field of the Invention
The present invention generally relates to high voltage devices, such as x-ray tubes. In particular, embodiments of the present invention relate to improvements for providing high voltage electrical connections within an x-ray tube environment.
2. The Related Technology
X-ray generating devices are extremely valuable tools that are used in a wide variety of applications, both industrial and medical. For example, such equipment is commonly employed in areas such as medical diagnostic examination and therapeutic radiology, semiconductor manufacture and fabrication, and materials analysis.
In a typical x-ray device, x-rays are produced when electrons are emitted, accelerated, and then impinged upon a material of a particular composition. This process typically takes place within an evacuated enclosure of an x-ray tube. Disposed within the evacuated enclosure is a cathode and an anode, which is oriented to receive electrons emitted by the cathode. The anode can be stationary within the tube, or can be in the form of a rotating annular disk that is mounted to a rotor shaft and bearing assembly. The evacuated enclosure is typically contained within an outer housing, which can also serve as a coolant reservoir in some implementations.
In operation, an electric current is supplied to a filament portion of the cathode, which causes a cloud of electrons to be emitted via a process known as thermionic emission. A high voltage potential is then placed between the cathode and anode to cause the cloud of electrons to form a stream and accelerate toward a focal spot disposed on a target surface of the anode. Upon striking the target surface, some of the kinetic energy of the electrons is released in the form of electromagnetic radiation of very high frequency, i.e., x-rays. The specific frequency of the x-rays produced depends in large part on the type of material used to form the anode target surface. Target surface materials with high atomic numbers (“Z numbers”) are typically employed. The target surface of the anode is oriented so that at least some of the x-rays are emitted through x-ray transmissive windows defined in the evacuated enclosure and the outer housing. The emitted x-ray signal can then be used for a variety of purposes, including materials analysis and medical evaluation and treatment.
As mentioned, in order to produce x-rays, tubes require that a large voltage differential exists between the anode and the cathode. This voltage differential is provided in a number of ways, depending on the type of x-ray tube. In cathode-grounded tubes, for instance, the anode is maintained at a relatively high voltage potential, while the cathode is held at ground potential. In anode-grounded tubes the reverse is true, wherein the cathode is held at high potential and the anode is grounded. In double ended tubes, both the anode and the cathode are maintained at relatively high voltages: the anode at high positive potential and the cathode at high negative voltage potential.
In any of the above types of x-ray tubes, it is necessary to provide at least one high voltage connection to the tube in order to supply the requisite voltage potential(s) to the table components. For example, in cathode-grounded tubes a high voltage electrode is connected to the anode via a connection at the end of the evacuated enclosure nearest the anode (i.e., the anode end of the tube) to provide voltage potential to the anode. In anode-grounded tubes, the high voltage electrode is connected to the cathode via a connection at the cathode end of the evacuated enclosure to provide the cathode with the requisite voltage potential. In double ended tubes, both of these types of connections are present.
Because of the high voltages that are present in the tube, measures must be taken to electrically isolate the evacuated enclosure from the rest of the x-ray device, and from other components disposed near the device. For instance, in some applications the x-ray device is located within a CT scanner that is used to produce radiographic images of a patient's body. The x-ray tube must be electrically isolated from both the x-ray device in which it is located, as well as the CT scanner itself to prevent damage or injury from occurring to the device, scanner, patient, or technician. In addition to insuring safety, adequate levels of electrical isolation are also needed to insure proper operation by the x-ray tube.
Various methods have been devised to electrically insulate the x-ray tube within the x-ray device. One method involves placing the evacuated enclosure of the x-ray tube within a fluid-tight outer housing, and filling the housing with a dielectric oil, thereby submerging the tube within the oil and insulating it from the outer housing of the x-ray device. While effective at electrically isolating the tube, this method nonetheless suffers from several drawbacks. First, fitting the x-ray device with a fluid tight outer housing for containing the dielectric oil involves substantial time and expense. The outer housing must be manufactured with special seals and other components so as to enable it to provide fluid containment during tube operation. This increases both the cost and complexity of the x-ray device.
Second, the presence of dielectric oil within the outer housing makes tube repair or device changeout more difficult and time consuming. This in turn limits the ability to maintain tube performance by prompt and proper maintenance. Moreover, because of its caustic nature, dielectric oil can cause degradation of tube components that are in contact with it, thereby shortening the operational life of the x-ray device. Also, because of the large amounts of thermal energy that are created by the tube during operation, the dielectric oil can absorb significant amounts of heat during tube operation. Heated oil increases the risk of leakage from the outer housing that contains it. Not only can this damage adjacent components, but it can also represent a potential hazard to the x-ray device itself and to those who operate it.
Another method has alternatively been used to electrically isolate the tube from the rest of the x-ray device. In some x-ray tubes, a potting material is attached to portions of the tube surface in order to insulate it. Using this method, the tube is first placed within the device housing or a jig structure. Potting material is then attached piece by piece to the tube surface as needed to insulate it. As with the dielectric oil, this method can also insulate the tube from the rest of the x-ray device. However, this method also suffers from several drawbacks. First, the piece by piece application of the potting material to the tube is time consuming, and thus raises manufacturing costs. Second, defects in the potting material may be detected only after application of the potting material to the tube surface is complete and initial testing of the x-ray tube is begun. If a defect is found, the potting material must be stripped from the tube, the tube cleaned, and the process begun again. Again, this wastes both time and materials and prolongs the assembly process.
In light of the above discussion, a need exists in the art for a means by which portions of a high voltage device, such as an x-ray tube, can be electrically isolated from a high voltage signal. Any solution should preferably be accomplished in a manner that does not require the extensive manufacturing steps that are required by prior art approaches. Moreover, the solution should obviate the use of messy and problematic dielectric oils in insulating the x-ray tube. In addition, any solution should not require significant time or expense when repair or changeout of tube components is necessary. Finally, any solution should present a relatively trouble-free resolution to the above challenges so as to reduce problems associated with the x-ray device and to ensure operational longevity for the tube, especially for tubes operated in harsh, high stress environments where reliable operation is especially important.